A Digital Micromirror Device™ (DMD™) is a type of microelectromechanical systems (MEMS) device. Invented in the 1980's at Texas Instruments Incorporated, the DMD is a fast, reflective digital light switch. Essentially, the DMD is an array of tiny tilting mirrors, each of which is individually addressable to an “on” (bright) or “off” (dark) state.
The DMD has a variety of applications, such as imaging systems and optical switching. For imaging systems, the DMD is combined with image processing, memory, a light source, and optics to form a digital light processing system capable of projecting large, bright, high-contrast color images.
DMD pixel's may have a variety of designs. One design has a mirror that is rigidly connected to an underlying yoke. The yoke in turn is connected by two thin, mechanically compliant torsion hinges to support posts that are attached to the underlying substrate. Electrostatic fields developed between the underlying memory cell and the yoke and mirror cause rotation in the positive or negative (on or off) rotation direction. Another design is “yokeless” and has an underlying hinge and spring tips on the same layer, and operates in response to electrostatic fields between the memory cell and the mirror.
For display applications, the DMD has an active pixel array and a perimeter of border pixels. The pixels of the active array are used to generate images by being tilted to either an “on” (bright) state or “off” (dark) state. The border pixels are always “off” so that they form a dark border around the active array.
The conventional approach to ensuring that the border pixels are always off is to hard wire the address electrodes under the mirror. When appropriate voltages are applied, the resulting electrostatic forces cause their mirrors to tilt in the off direction.